The present invention relates to integrated circuit (IC) test fixtures and, in particular, to flexible contact termination circuits usable therewith and configured from flexible printed circuits containing conductive pathways of tailored X, Y and Z-axis profiles. The circuit and pathways are constructed to provide predetermined impedance characteristics, include spaced, resilient contact terminations, and operate at gigahertz frequencies.
A fundamental requirement of electrical test fixturing is to repeatably and at high speeds make electrical contact to the lead terminations of circuit components admitted to the test fixturing. As each component is admitted, one or more contact assemblies make electrical contact to each or selected ones of the termination leads at the component. A resilient connection is preferred to accommodate packaging variations, yet achieve a good electrical contact with the component.
Numerous, commercially available test fixtures and contact assemblies provide discreet spring metal terminals which are separately staked and/or soldered to a contact assembly. Associated printed circuit pathways at a termination circuit of the assembly convey input/output signals from and to the components under test.
Although adequate for many types of components, discreet contact terminals necessitate relatively costly termination circuit assemblies, due to a necessity of separately staking and/or soldering each contact to the conductive pathways. The physical size of such terminals presents practical limits to the physical spacing attainable relative to the pin spacing and pin arrangement at a component under test and can affect the organization of the test fixture. The coupling interface between the terminals and signal paths also effect electrical performance and limit testing to frequencies well below the gigahertz range attainable with the present invention. Certain limits therefore exist to the types of components which can be tested and on occasion multiple fixturings and test passes may be required to test a single component. The corresponding fabrication complexity and necessity to separately inventory many uniquely configured contact assemblies for specific types of components to be tested further limits the flexibility of many test fixtures.
The use of discreet conductive paths and contacts also introduces signal impedance characteristics which can affect and limit the capability of many test fixtures to test certain circuits at operating frequencies. The latter difficulties are especially critical for test fixtures intended for use with components operating at frequencies in excess of 100 MHz and into the gigahertz range, which components are becoming increasingly more common.
As increasingly greater complexity has been integrated into most typical components, greater varieties of non-standard packaging configurations and types of lead terminations and lead arrangements have also appeared. The organization and presentation of such terminations about a component's periphery can vary widely. Terminal counts from 12 to 100 per side, per device can be encountered at various termination spacings. The termination organizations may be organized in standard arrangements to non-uniform or non-symmetric geometrical arrangements at multiple peripheral surfaces of a component package. The terminations may take the form of relatively rigid leads such as conventional SIP and DIP components, to gull wing terminations, to a variety of fine pitch QFP, PQFP/TQFP, SOP/TSOP, PLCC terminations, among others.
In appreciation of the increasing complexities of components being used to populate printed circuit assemblies, it is therefore preferred that any component test fixture be adaptable to accommodate a wide range of components. It is a further desire that each test point of any test fixture exhibit a known electrical characteristic from the point of contact to a component over the entire conductive pathway and to the test monitor. The latter attributes are met with the inventive termination circuits and fixturing of the present invention.
Test circuits which exhibit discreet, separately staked or soldered connections can be found at U.S. Pat. Nos. 4,686,463; 4,853,626; 4,965,865; and 5,121,053. The latter patents also disclose a variety of test fixtures which are compatible with different component packaging.
Other test assemblies of some relevance to the present invention are shown at U.S. Pat. Nos. 4,998,062; 5,091,694; 4,018,491; 4,472,876; 4,554,505; and 4,686,468. Various of these references depict fixtures which contain contact assemblies having conductive pathways which terminate at spaced apart, comb-like contacts which integrally extend from printed circuit pathways. The contact terminations and associated pathways are constructed to uniform thickness and are fabricated using conventional PC fabrication techniques.
The pathways may include additional plating to add thickness, for example, at selected through hole vias. Resilient support assemblies are included with various of the test fixtures to resiliently support each contact. The contacts otherwise are not particularly constructed to provide independent resilience.
U.S. Pat. No. 4,085,502 also discloses a method and flexible circuit structures which include "plated-up" mesas that are etched to form rigid, integral terminations. The terminals are intended for mounting to PC boards and are not constructed to provide any inherent resilience.
In appreciation of the foregoing deficiencies in the art, the present invention provides test fixtures and contact termination circuits usable therewith which provide electrically uniform, contiguous, conductive pathways that are "etched down" to preferred three-dimensionally sculptured shapes. The termination circuits are constructed using conventional printed circuit fabrication techniques, yet facilitate an ability to economically construct wide varieties of special purpose and custom test assemblies. The termination circuits can be prepared to pre-determined impedance and resilience characteristics, and permit operating frequencies into the gigahertz range. The circuits readily mount to existing and custom developed component test fixtures. As necessary, additional resilience can be provided at the test fixture with a resilient component support surface.